bjoernager/rust
bjoernager/rust
1
Fork 0
Code Issues Pull requests Activity

Validate unsize coercion in MIR validation

Browse source
This commit is contained in:
Michael Goulet 2024-09-23 03:56:20 -04:00
parent 38352b01ae
commit 8fc8e03150
4 changed files with 100 additions and 29 deletions
Download patch file Download diff file Expand all files Collapse all files

50
compiler/rustc_mir_transform/src/validate.rs
View file

@ -4,7 +4,8 @@ use rustc_data_structures::fx::{FxHashMap, FxHashSet};
use rustc_hir::LangItem;
use rustc_index::IndexVec;
use rustc_index::bit_set::BitSet;
use rustc_infer::traits::Reveal;
use rustc_infer::infer::TyCtxtInferExt;
use rustc_infer::traits::{Obligation, ObligationCause, Reveal};
use rustc_middle::mir::coverage::CoverageKind;
use rustc_middle::mir::visit::{NonUseContext, PlaceContext, Visitor};
use rustc_middle::mir::*;
@ -16,6 +17,8 @@ use rustc_middle::ty::{
use rustc_middle::{bug, span_bug};
use rustc_target::abi::{FIRST_VARIANT, Size};
use rustc_target::spec::abi::Abi;
use rustc_trait_selection::traits::ObligationCtxt;
use rustc_type_ir::Upcast;
use crate::util::{is_within_packed, relate_types};
@ -586,6 +589,22 @@ impl<'a, 'tcx> TypeChecker<'a, 'tcx> {
crate::util::relate_types(self.tcx, self.param_env, variance, src, dest)
}
/// Check that the given predicate definitely holds in the param-env of this MIR body.
fn predicate_must_hold_modulo_regions(
&self,
pred: impl Upcast<TyCtxt<'tcx>, ty::Predicate<'tcx>>,
) -> bool {
let infcx = self.tcx.infer_ctxt().build();
let ocx = ObligationCtxt::new(&infcx);
ocx.register_obligation(Obligation::new(
self.tcx,
ObligationCause::dummy(),
self.param_env,
pred,
));
ocx.select_all_or_error().is_empty()
}
}
impl<'a, 'tcx> Visitor<'tcx> for TypeChecker<'a, 'tcx> {
@ -1202,8 +1221,33 @@ impl<'a, 'tcx> Visitor<'tcx> for TypeChecker<'a, 'tcx> {
}
}
CastKind::PointerCoercion(PointerCoercion::Unsize, _) => {
// This is used for all `CoerceUnsized` types,
// not just pointers/references, so is hard to check.
// Pointers being unsize coerced should at least implement
// `CoerceUnsized`.
if !self.predicate_must_hold_modulo_regions(ty::TraitRef::new(
self.tcx,
self.tcx.require_lang_item(
LangItem::CoerceUnsized,
Some(self.body.source_info(location).span),
),
[op_ty, *target_type],
)) {
self.fail(location, format!("Unsize coercion, but `{op_ty}` isn't coercible to `{target_type}`"));
}
// FIXME: Codegen has an additional assumption, where if the
// principal trait def id of what's being casted doesn't change,
// then we don't need to adjust the vtable at all. This
// corresponds to the fact that `dyn Tr<A>: Unsize<dyn Tr<B>>`
// requires that `A = B`; we don't allow *upcasting* objects
// between the same trait with different args. Nothing actually
// validates this, though. While it's true right now, if we for
// some reason were to relax the `Unsize` trait, it could become
// unsound. We should eventually validate that, but it would
// require peeling `&Box<Struct<.., dyn Tr<A>, ..>>` down to
// the trait object that's being unsized, and that's rather
// annoying, and also it would need to be opportunistic since
// this MIR is not yet fully monomorphized, so we may bottom
// out in an alias or a projection or something.
}
CastKind::PointerCoercion(PointerCoercion::DynStar, _) => {
// FIXME(dyn-star): make sure nothing needs to be done here.